Robot system

Abstract

A robot system includes a plurality of claw members movably provided in a hand and configured to hold and release a workpiece. Further, one or more servo motors is provided to move the claw members. A controller controls an operation of each of the servo motors. The controller includes an acquisition unit configured to acquire dimension information of the workpiece, a position control unit configured to perform position control on the servo motors so that the claw members move to first positions and then to second positions pursuant to the dimension information, and a torque limiting unit configured to limit a torque command relating to each of the servo motors to a predetermined torque or less after the claw members are moved to the first positions.

What is claimed is: 
     
         1 . A robot system, comprising:
 a robot;   a hand provided in the robot;   a plurality of claw members movably provided in the hand and configured to hold and release a workpiece;   one or more servo motors configured to move the claw members; and   a controller configured to control an operation of each of the servo motors,   wherein the controller includes an acquisition unit configured to acquire dimension information of the workpiece, a position control unit configured to perform position control on the servo motors so that the claw members move to first positions and then to second positions pursuant to the dimension information, and a torque limiting unit configured to limit a torque command relating to each of the servo motors to a predetermined torque or less after the claw members are moved to the first positions.   
     
     
         2 . The robot system of  claim 1 , wherein the first positions are positions where the claw members are just prior to making contact with the workpiece in order to hold the workpiece, and wherein the second positions are positions closer to the center of the workpiece than the first positions. 
     
     
         3 . The robot system of  claim 2 , wherein the controller further includes a speed control unit configured to control the claw members so that the speed at which the claw members move to the first positions becomes higher than the speed at which the claw members move from the first positions to the second positions. 
     
     
         4 . The robot system of  claim 3 , wherein each of the claw members includes a bottom plate and a side plate formed at a predetermined angle with respect to the bottom plate,
 wherein the claw members are arranged in one pair so that the side plates of the claw members face each other, and   wherein the workpiece is placed on the bottom plates of the claw members and pinched and held by the side plates of the claw members.   
     
     
         5 . The robot system of  claim 4 , wherein each of the claw members includes, at a tip end of the bottom plate, a taper portion formed on a surface opposite to a surface on which the workpiece is placed. 
     
     
         6 . The robot system of  claim 4 , wherein the number of the servo motors is two, and the two servo motors are arranged in a corresponding relationship with the claw members, and wherein the position control unit performs position control on the two servo motors so that, when holding the workpiece, the claw members are moved together and so that, when releasing the workpiece, one of the claw members is kept stationary and the other is moved. 
     
     
         7 . The robot system of  claim 5 , wherein the number of the servo motors is two, and the two servo motors are arranged in a corresponding relationship with the claw members, and wherein the position control unit performs position control on the two servo motors so that, when holding the workpiece, the claw members are moved together and so that, when releasing the workpiece, one of the claw members is kept stationary and the other is moved. 
     
     
         8 . The robot system of  claim 4 , further comprising:
 at least one pusher provided in the hand and configured to relatively move the workpiece placed on the bottom plate with respect to the claw members; and   at least one additional servo motor configured to drive the pusher,   wherein the acquisition unit is configured to acquire information on a placing position of the workpiece, the position control unit is configured to perform position control on the additional servo motor so that, when releasing the workpiece and withdrawing the claw members from the workpiece, the pusher keeps the workpiece in the placing position.   
     
     
         9 . The robot system of  claim 5 , further comprising:
 at least one pusher provided in the hand and configured to relatively move the workpiece placed on the bottom plate with respect to the claw members; and   at least one additional servo motor configured to drive the pusher,   wherein the acquisition unit is configured to acquire information on a placing position of the workpiece, the position control unit is configured to perform position control on the additional servo motor so that, when releasing the workpiece and withdrawing the claw members from the workpiece, the pusher keeps the workpiece in the placing position.   
     
     
         10 . The robot system of  claim 6 , further comprising:
 at least one pusher provided in the hand and configured to relatively move the workpiece placed on the bottom plate with respect to the claw members; and   at least one additional servo motor configured to drive the pusher,   wherein the acquisition unit is configured to acquire information on a placing position of the workpiece, the position control unit is configured to perform position control on the additional servo motor so that, when releasing the workpiece and withdrawing the claw members from the workpiece, the pusher keeps the workpiece in the placing position.   
     
     
         11 . The robot system of  claim 7 , further comprising:
 at least one pusher provided in the hand and configured to relatively move the workpiece placed on the bottom plate with respect to the claw members; and   at least one additional servo motor configured to drive the pusher,   wherein the acquisition unit is configured to acquire information on a placing position of the workpiece, the position control unit is configured to perform position control on the additional servo motor so that, when releasing the workpiece and withdrawing the claw members from the workpiece, the pusher keeps the workpiece in the placing position.   
     
     
         12 . The robot system of  claim 1 , further comprising:
 a conveyor configured to convey the workpiece to a holding position where the workpiece is held by the claw members; and   a transport container on which the workpiece released from the claw members is to be placed and to which the claw members are accessible in a direction perpendicular to a workpiece conveyance direction of the conveyor.   
     
     
         13 . The robot system of  claim 11 , further comprising:
 a conveyor configured to convey the workpiece to a holding position where the workpiece is held by the claw members; and   a transport container on which the workpiece released from the claw members is to be placed and to which the claw members are accessible in a direction perpendicular to a workpiece conveyance direction of the conveyor.   
     
     
         14 . The robot system of  claim 12 , wherein, when moving the hand to a third position where the workpiece is placed on the transport container, the hand rotates about a second rotation axis which is parallel to a first rotation axis of the hand and which is positioned closer to the workpiece than the hand and moves to the third position. 
     
     
         15 . The robot system of  claim 13 , wherein, when moving the hand to a third position where the workpiece is placed on the transport container, the hand rotates about a second rotation axis which is parallel to a first rotation axis of the hand and which is positioned closer to the workpiece than the hand and moves to the third position. 
     
     
         16 . The robot system of  claim 14 , wherein the controller further includes a setting unit configured to set a position of the second rotation axis based on the dimension information of the workpiece. 
     
     
         17 . The robot system of  claim 15 , wherein the controller further includes a setting unit configured to set a position of the second rotation axis based on the dimension information of the workpiece. 
     
     
         18 . The robot system of  claim 14 , wherein, when moving the hand to the third position where the workpiece is placed on the transport container, the hand moves to the third position by translating the second rotation axis and then rotating about the second rotation axis. 
     
     
         19 . The robot system of  claim 12 , wherein the conveyor includes a lift device configured to stop the workpiece in the holding position and lift up the workpiece. 
     
     
         20 . The robot system of  claim 1 , wherein the workpiece is a cardboard box.